1. Field of the Invention
The present invention relates to a tracking type photovoltaic power generator and an error correction method of its built-in clock.
2. Description of the Related Art
Conventionally, a tracking type photovoltaic power generator has been well known. This tracking type photovoltaic power generator, as conceptually shown in FIG. 1, has a power generation module 12 supported so as to be rotatably in a direction of an azimuth angle xe2x80x9cAxe2x80x9d and a direction of an elevation angle xe2x80x9cZxe2x80x9d. Also, this tracking type photovoltaic power generator has a sun direction sensor rotated together with the power generation module 12, a clock and a controller although they are not shown. A signal obtained from the sun direction sensor for indicating a sun direction is sent to the controller.
This conventional tracking type photovoltaic power generator uses the following two methods to detect the sun direction. In the first method, the sun direction is detected by the calculation based on a position (represented by a longitude and a latitude) at which the tracking type photovoltaic power generator is installed, and a date and a time. In this case, the date and the time are obtained from the clock. In the second method, the sun direction is detected based on a signal from the sun direction sensor.
This conventional tracking type photovoltaic power generator is operated as follows. That is, on an arrival of an operation start time (for example, a time of a sunrise), the power generation module 12 is firstly turned to the sun direction. That is, the controller detects the sun direction by using the first method, and rotates the power generation module 12 to the detected direction.
In the normal operation after that, if the sun is behind a cloud, the first method is used to detect the sun direction at a predetermined time interval. If the sun is not behind the sun, the second method is used to detect the sun direction at the predetermined time interval. Based on those detected results, the power generation module 12 is rotated at the predetermined time interval so that a light reception surface of the power generation module 12 is faced to the sun. Thus, it is controlled such that the light reception surface of the power generation module 12 is always opposite perpendicularly to the sun, namely, the power generation module 12 tracks the sun.
By the way, a quartz oscillation clock similar to a home clock is used as the above-mentioned clock. An error (an oscillation stability) of this clock is 11 ppm (corresponding to one second/day) if an ambient temperature is 10 to 30xc2x0 C. Also, if the ambient temperature is xe2x88x9240 to 85xc2x0 C., the error is 150 ppm (13 seconds/day). If it is converted into an annual error, the error becomes 80 minutes/year.
The occurrence of such an error causes the direction of the light reception surface of the power generation module 12 to be deviated from the actual sun direction. For example, the delay of the clock such as two minutes and fifty seconds may cause the following situation. That is, as shown in FIG. 2, although a culmination time (also referred to as xe2x80x9cmeridian passage timexe2x80x9d) determined by a calculation is forty minutes thirty seconds past eleven, a time when the light reception surface of the power generation module 12 is turned to a true south in the case of the tracking operation using the sun direction sensor is forty-three minutes twenty seconds past eleven. The excessively large deviation causes the sun to depart from a visual angle of the sun direction sensor, when the control based on the sun direction detected by the first method is switched to the control based on the sun direction detected by the second method. Thus, there may be the case that the tracking is impossible.
This error of the clock can be manually corrected by a person at the position of the installation of the tracking type photovoltaic power generator. However, if the installation position of the tracking type photovoltaic power generator is located at a remote place, various difficulties are brought about.
Therefore, an object of the present invention is to provide a tracking type photovoltaic power generator that can automatically correct an error of a clock, and an error correction method of its built-in clock.
In order to attain the above-mentioned object, a tracking type photovoltaic power generator according to a first aspect of the present invention comprises a clock for clocking a time, a sun direction sensor and a controller. The sun direction sensor outputs a signal indicative of a sun direction. The controller corrects an error of the time clocked by the clock based on the signal from the sun direction sensor.
In the tracking type photovoltaic power generator according to the first aspect of the present invention, the controller may be composed of a calculating section, a detecting section and a correcting section. The calculating section calculates a first time when the sun arrives at a predetermined azimuth based on the time clocked by the clock. The detecting section detects the predetermined azimuth based on the signal from the sun direction sensor. The correcting section corrects the error of the time clocked by the clock based on a difference between a second time when the detecting section detects the predetermined azimuth and the first time calculated by the calculating section.
In this case, the detecting section can be configured so as to detect the predetermined azimuth based on the signal from the sun direction sensor within a predetermined time period before or after the first time calculated by the calculating section. Also, the correcting section can be configured so as to correct the error of the time clocked by the clock in a time band except the predetermined time period. Moreover, the correcting section can be configured so as to correct the error of the time 6.
An error correction method of its built-in clock in the tracking type photovoltaic power generator according to a second aspect of the present invention includes the steps of: detecting an error of a time clocked by the built-in clock based on a signal from a sun direction sensor; and correcting the error of the time clocked by the built-in clock based on the detected error.
In the error correction method of its built-in clock in the tracking type photovoltaic power generator according to the second aspect of the present invention, the step of detecting the error can be composed so as to include the steps of: calculating a first time when the sun arrives at a predetermined azimuth based on the time clocked by the built-in clock; detecting the predetermined azimuth based on the signal from the sun direction sensor; and detecting the error of the time clocked by the built-in clock based on a difference between a second time when the predetermined azimuth is detected and the calculated first time.
In this case, the correcting step can be configured so as to correct the error of the time clocked by the built-in clock when the difference becomes equal to or greater than a predetermined value.